The present invention relates generally to medical devices and, more particularly, to a radioactive medical device having radiation emitting capabilities for inhibiting an undesired hyperplastic response to the healing of biological tissue, and a method for making and using the devices.
In patients with vascular disease, cardiovascular surgeons use sutures to anastomose autogenous vein, prosthetic grafts, or arteries to other arteries in order to bypass around or replace diseased vessel segments. At virtually all anastomotic sites between the arteries, veins, and autogenous vein, or prosthetic grafts, a condition of rapid cellular growth termed xe2x80x9cintimal hyperplasiaxe2x80x9d may occur.
Intimal hyperplasia is the usual response to blood vessel injury. This rapid cellular growth, as a response to injury of the blood vessel cellular lining, begins to narrow the opening between the vessels and/or graft to the point where an occlusion may occur. More specifically, intimal hyperplasia forms as a result of smooth muscle cell proliferation, migration, and extracellular matrix deposition. The interaction of platelets, macrophages, growth factors, and cytokines plays an important role in the process. Intimal hyperplasia is one of the primary cause of xe2x80x9crestenosisxe2x80x9d (narrowing) in the first year after vascular bypass operations. Usually, the patient must have another operation to revise or replace the occluded graft. If a major vein occludes (e.g. jugular or subclavian) massive edema of the upper extremity, face and neck may occur. If a limb artery occludes, it could possibly lead to potential limb loss.
Of course, intimal hyperplasia is merely a subset of a larger problem involving hyperplasia resulting from smooth muscle cell proliferation, migration, and extracellular matrix deposition. In general, when biological tissue begins grafting, or healing, an undesirable hyperplastic response may occur. It would be desirable to limit, or even prevent such an unwanted hyperplastic response.
One of the most frequently performed vascular surgical operation is an arterial to venous conduit for dialysis in chronic renal failure patients. Renal dialysis patients require repetitive angioaccess to this arterial-venous conduitive graft for dialysis to rid their system of the body""s toxins. The most commonly used graft for dialysis in the United States is a prosethetic graft made from teflon or ePTFE (expanded polytetrafluroethylene). Unfortunately, as a consequence of repeated access by dialysis needles, these grafts fail frequently and have a primary occlusion rate of 15% to 50% during the first year, with a mean patency of only 15 months. One of the most common causes of failure in these grafts is due to the development of intimal hyperplasia at the venous anastomosis. Again, there is a strong desire in the art to prevent this unwanted hyperplastic response.
Both examples of tissue grafting stated above, operations necessary to treat arterial occlusive disease and an arterial to venous conduit for dialysis, prescribe the use of a suture to assist the healing of biological tissue. However, there are several devices currently used in the medical field for assisting the grafting of biological tissue. Amongst which may be, xe2x80x9cpatches,xe2x80x9d xe2x80x9cwraps,xe2x80x9d and meshes which give the tissues time to heal. Similarly, stents come in a variety of configurations for supporting blood vessel walls in an attempt to inhibit stenosis of the vessel.
Surgical sutures are used to bring together ends of biological tissue and hold them in place until the joining tissues have time to heal. As another example, in some types of medical operations, medical personnel may use xe2x80x9cpatchesxe2x80x9d or meshes to support tissue in order to give the tissue appropriate time to heal. Just as with vascular bypass conduits, the tissue adjacent the xe2x80x9cpatchxe2x80x9d or mesh may also exhibit signs of hyperplasia that are undesirable, if not harmful.
In recent years, studies have been conducted in animal models whose vessels have undergone balloon angioplasty. It was found that the vessels response to injury from balloon angioplasty is similar to that observed at suture anastomotic sites. Studies conducted at Emory University, Atlanta, Ga., U.S.A., and Vanderbilt University, Nashville, Tenn., U.S.A., suggest that restenosis results primarily from the migration and rapid proliferation of a smooth muscle type cell after balloon angioplasty. It has been demonstrated by these groups that very low levels of beta-particle irradiation introduced to the site of injury following angioplasty markedly inhibits smooth muscle cell proliferation and or migration. Numerous other studies have been conducted which have demonstrated and substantiated these early findings.
U.S. Pat. No. 5,897,573, filed Apr. 22, 1997, dealt with the problem of unwanted hyperplastic response in biological tissue by suggesting the irradiation of a suture material prior to its use in a patient. U.S. Pat. No. 5,897,573 describes how a low-level beta-emitting radioisotope may be incorporated into the chemical structure of suture material in order to inhibit an unwanted hyperplastic response. U.S. Pat. No. 5,897,573, filed Apr. 22, 1997, is hereby incorporated by reference as if fully set out herein.
Similarly, U.S. Pat. No. 6,042,600, filed Jan. 25, 1999, dealt with the problem of unwanted hyperplastic response in biological tissue by suggesting the irradiation of various medical devices before use in a patient. U.S. Pat. No. 6,042,600 was a continuation in part of U.S. Pat. No. 5,897,573. U.S. Pat. No. 6,042,600 describes how a low-level beta-emitting radioisotope may be incorporated into the chemical structure of a medical device. U.S. Pat. No. 6,042,600, filed Jan. 25, 1999, is hereby incorporated by reference as if fully set out herein.
Both of the two above-described patents generally prescribe chemically bonding the radioactive element to the structure of the medical device. However, there may be situations where it is not desirable to alter the chemical structure of the medical device to be used. Additionally, certain isotopes may not readily lend themselves to chemically attaching themselves to the molecules of the medical device. To remedy this need, U.S. Pat. Application having Ser. No. 09/711,766 was filed on Nov. 13, 2000. This patent application, also deals with radioactive medical devices. However, the devices are created by a process involving occluding salts of radioacitve isotopes into a molecular matrix of the medical device. U.S. Pat. Application having Ser. No. 09/711,766, filed Nov. 13, 2000, is hereby incorporated by reference as if fully set out herein.
Generally described, the present invention provides a radioactive medical device having radiation emitting capabilities for inhibiting an undesired hyperplastic response to the healing of biological tissue, and a method for making and using the devices. It is known that smooth muscle cell proliferation may be inhibited by varying degrees and types of radiation, particularly low level beta radiation and low level gamma radiation. This knowledge is exploited by the radioactive medical devices and method described herein.
In a first preferred embodiment, a method of creating a medical device that inhibits a hyperplastic response in biological tissue comprises the following steps: providing a first solvent in a container; introducing a salt or an acid of a radioactive isotope into the first solvent such that the salt or acid disassociates into ionic components so as to form a first solution; introducing a second solvent into the first solution so as to form a second solution; and introducing the medical device into the second solution, wherein the ionic components migrate from the second solution into the molecular structure of the medical device.
In another aspect, a method of creating a medical device that inhibits a hyperplastic response in biological tissue comprises the following steps: providing an organic solvent in a container; introducing a salt or an acid of a radioactive isotope into the organic solvent such that the salt or acid disassociates into ionic components so as to form a solution; and introducing the medical device into the solution, wherein the ionic components migrate from the solution into the molecular structure of the medical device.
In another aspect, a method of creating a medical device that inhibits a hyperplastic response in biological tissue comprises the following steps: providing an aqueous solution in a container; introducing a salt or an acid of a water soluble radioactive isotope into the aqueous solution such that the salt or acid disassociates into ionic components so as to form a second solution; and introducing the medical device into the second solution, wherein the ionic components migrate from the solution into the structure of the medical device.
In a first preferred embodiment of a medical device for inhibiting a hyperplastic response in biological tissue, the medical device generally comprises polymeric hydrocarbon molecules forming the medical device and a salt or an acid of a radioactive isotope occluded within the polymeric hydrocarbon molecules. As a result of this structure, the radioactive isotope in the polymeric hydrocarbon molecules of the medical device inhibits a hyperplastic response in biological tissue.
In another aspect of a medical device for inhibiting a hyperplastic response in biological tissue, the medical device comprises a thrombogenic sponge-like material having a radioactive isotope trapped within the structure of the sponge-like material. As a result of this structure, the radioactive isotope inhibits a hyperplastic response in biological tissue.
Other systems, methods, features, and advantages of the present invention will be or will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.